Made by GM, casting dates are represented by a letter (month, "A" = January, "B"= February, "I" is not used) two digits (day of month) and a single digit (last digit of year)My block is a 12555506 and the Date code is M039
These numbers came off the driver and passenger back of engine behind the heads.
Who made the blocks with the M039 or does anyone know what it is?
"I" could be mistaken for "1", so is not used. "M" = 12th month.So my block is at risk of having the number 8 cylinder problems?
Why dont they use I?
#8 cylinder is not the problem with that block, its the bottom end cracking through the piston squirters into the water jacket that it is highly prone to and the 99-2001 gm blocks changed the main caps and were prone to breaking the #2 main cap in half.So my block is at risk of having the number 8 cylinder problems?
Why dont they use I?
the tooling did not cause it, it was gm taking them right from the foundry and machining them without letting them cure first to keep up with the demand, as they cured after being machined it then had the stress risers.'Engine Builder' magazine did an article on the GEP Optimizer back in June 2007: http://www.enginebuildermag.com/Article/1458/the_optimizer_6500.aspx (article is supported with photos)
In the article they discussed some of the main problems with the GM 6.5 blocks. Although the article doesn't reference particular block #'s, in some cases you can infer which blocks are being discussed based on the design description given, e.g; Piston Cooling Jets:
"While machining for piston oiler holes in the main bearing saddles, tooling would occasionaly contact the bottom of the cylinder bores, causing stress risers that have led to cracking"
If I'm not mistaken, the only 6.5 diesel blocks produced by GM with the oiler jets was the 506. - Apparently though, not all 506 blocks were affected, as it was an "occasional" problem - Luck of the draw there I guess.
the info came directly from bill heath, from what i remember from the conversation when i called about my 506 block and girdles (he says stay far away from them btw)they need to cure because as the casting cools and hardens the metal still shifts, if not allowed to cure fully and is machined it then distorts as it finishes curingThat's interesting, I didn't know that freshly cast engine blocks needed time to cure. Why exactly do they need to cure? How much time do they typically need?
The article is fairly persuasive as it has a photo of (allegedly) a 506 block showing a tooling 'nick' at the bottom of the cylinder bore.
I'm curious to know how you learned about this? There's so much misinformation out there it can be vexing to sort the facts from the myths, especially when two totally differing accounts seem equally plausible.
If it is possible, check in the valley of your block, to see if the Navistar emblem is cast in to it. Also, should have 506 cast (with dots) on the side of the valley...... if you could post up some pics with the intake removed, it would aid us, as our info is a little sketchy. Without the pics, the best we can do is; 2005 March 9.
Hoping mine is a #141#141 block casting was in late 1996 truck production. My march 96 assembled 96 has one in it. It has been an absolutly stable block/heads. ,now over 180.00 miles.& has factory dual thermostats.To my knowledge NO Navastar blocks were installed in the regular production trucks. They were supplied in some warranty paid replacements around Y2K.